Cantilever beams micro-machined in silicon are currently used as displacement sensors in such devices as atomic force microscopes, magnetic force microscopes and other force based scanning probe techniques where force applied to the cantilever causes a physical displacement that is detected. Cantilever beams are also used to sense vibrations of structures, inertial force, and to detect mass of the cantilever itself.
Cantilever displacement or deflection has been detected by several different methods. The methods include deflection of an external laser beam reflecting off of the cantilever, piezoresistive measurements, capacitance change between cantilever and substrate, and measurement of tunneling current. These methods suffer from various disadvantages relating to their use as sensitive mass sensors due to complex mounting requirements, lack of sensitivity, difficult fabrication, and environmental instability.
The ability to detect small amounts of materials, including pathogenic bacteria and biomolecules integral to cell responses, is important for life science research, drug discovery, medical diagnostics and for homeland security. Most current detection technologies are either, bulky, expensive or slow. Current instrumentation for single molecule detection is largely based upon direct optical measurements which provide a limited ability to interrogate an unknown molecule. Spectroscopic techniques such as ultraviolet, infrared (IR) and fluorescence all operate based upon the intrinsic spectral properties of the molecule alone or in combination with a label. The ability of these techniques to be informative is limited and this is especially true of molecules with a limited unique optical spectra and where there are a number of molecules in the milieu with similar spectral signatures.
Other methods of detecting biomolecules when attached to an antibody including those that might be a biowarfare agent, using integrated optics have been demonstrated recently. However, these depend on tight fabrication tolerances due to the efficient coupling and single wavelength operation of the sensing device, normally ring or disk resonators. Also, these techniques require expensive accessories, as single wavelength lasers are required and are tuned to the fabricated device.